BIND9.4.1 : forwarding not working

Hello,
For some odd reasong i setup a forwarder zone a couple months ago and all has been woorking fine, except now. The forward requests sometimes responds with an IP address. Here's a captue from the bind log in debug mode, i hope someone can explain to me what going on? thnx

Found out more info.
Apparently 2 of 4 destination nameservers have the A/PTR records. I thought that when you configure a zone for forwarding that it would "round robin" through all the nameservers in the list until it gets a response?